1. Field of the Invention
The present invention relates to an immobilizer device for a vehicle or the like, and more particularly to such an immobilizer device which can rapidly authenticate a password without using a high-speed CPU.
2. Description of the Background Art
There is known an immobilizer device which is used as a vehicle theft prevention device. Generally, the immobilizer device is constituted of a key which incorporates a transponder (transmitter/responder) therein, an immobilizer ECU and an engine ECU. When electricity is supplied to the immobilizer device, the immobilizer ECU transmits a request signal which contains random numbers to the key. When the key transponder receives the random numbers, the transponder generates a password by using the received random numbers and a functional formula and transmits the password to the immobilizer ECU. The immobilizer ECU collates by comparison a password relating to the random numbers which were transmitted by the immobilizer ECU with the password received from the transponder. Further, when it is determined that these passwords agree with each other as a result of the collation, the immobilizer ECU inputs preset simple identification information (ID) to the engine ECU. The engine ECU stores an ID which is identical with the ID preset in the immobilizer ECU. When it is determined that these IDs agree with each other as a result of the collation, the engine ECU starts a scheduled fuel supply control and ignition control. When it is determined that the password is wrong as the result of the password collation by the immobilizer ECU, the ID is not inputted to the engine ECU from the immobilizer ECU and hence, the fuel supply control and the ignition control are inhibited whereby starting of an engine is not permitted.
With respect to the above-mentioned known background art, for further enhancing the security performance, it is preferable to perform the collation of passwords between the immobilizer ECU and the engine ECU. An immobilizer device which performs the collation of passwords between an immobilizer ECU and an engine ECU as a second stage of authentication is disclosed in JP-A-2000-108848, for example.
However, the two-stage authentication in which the collation of passwords is performed between a key transponder and the immobilizer ECU and, at the same time, the collation of passwords is also performed between the immobilizer ECU and the engine ECU has a drawback that it takes time until the engine assumes an engine start permission state after an ON operation of an ignition switch is performed. Although it may be possible to mount a high speed CPU on the immobilizer ECU for shortening the password collation time, mounting of the high-speed CPU will likely increase the cost of the immobilizer device.
Therefore, it is therefore an object of the present invention to provide an immobilizer device which can overcome the above-mentioned drawbacks and can enhance the theft prevention performance of a vehicle without using a high-speed CPU.